Field of the Invention
The present invention relates to a recording medium, near field optical head, and optical recording device capable of utilizing near field light to record and reproduce information in a highly precise manner, and to a manufacturing method thereof.
Typically, Scanning Probe Microscopes (SPMs) are used in Scanning Tunnel Microscopes (STMs) and Atomic Force Microscopes (AFMs) for monitoring microscopic regions in the order of a few nanometers of a sample surface, An SPM monitors a sample surface with a probe having a pointed tip. Mutual interaction of tunnel currents and interatomic forces occurring between the probe and the sample surface are then taken as subjects of monitoring and an image of a resolution depending upon the shape of the probe tip can be obtained, This does, however, place relatively severe constraints on the sample being monitored.
Near field optical microscopes where the subject of the monitoring is taken to be the mutual interaction occurring between the near field light generated at the sample surface and the probe so that it is possible to monitor microscopic regions of the sample surface have recently come to the forefront.
With these near field optical microscopes, propagating light illuminates the surface of the sample so as to generate near field light. Near field light generated in this manner is then scattered by a probe with a pointed tip and this scattered light is processed in the same manner as the detection of propagated light in the related art. This eliminates the boundaries in monitoring resolution of related optical microscopes and enables observation of even more microscopic regions. The observation of the optical properties of the sample occurring at microscopic regions can therefore by achieved by sweeping the wavelength of the light the sample surface is illuminated with.
In addition to utilization as a microscope, applications are also possible in high-density optical memory recording where near field light of a high energy density is generated at a microscopic opening of the optical fiber probe by introducing light of relatively substantial intensity to the sample via the optical fiber probe so as to cause the structure or the physical properties of the sample surface to be changed in a localized manner by this near field light.
Cantilever optical probes as disclosed, for example, in U.S. Pat. No. 5,294,790 where an opening passing through a silicon substrate is formed using semiconductor manufacturing technology such as photolithography etc., an insulation film is formed on one side of the silicon substrate, and a conical optical waveguide layer is formed on the insulation film on the opposite side to the opening have also been put forward as probes for use in near-field optical microscopes. With this kind of cantilever-type optical probe, an optical fiber is inserted into the opening, and light is made to pass through a microscopic opening formed by coating everything but the tip of the optical waveguide layer with a metal film.
The use of flat probes that do not have pointed tips as the aforementioned probes do has also been proposed. This plane probe is formed with an opening having a conical structure, by anisotropic etching of a silicon substrate, with a vertex that is a few tens of nanometers across which can be passed through. Making a plurality of plane probes of this structure on the same substrate using semiconductor manufacturing technology, i.e. making an array of plane probes, is straightforward and utilization in optical memory heads for reproducing and recording optical memory using near field light is possible. Flying heads as used in related hard discs and having plane probes have also been put forward as optical heads employing this plane probe. Such flying heads are designed such that aerodynamic force causes the heads to float 50 to 100 nanometers from the recording medium. A microscopic opening is formed in the recording medium side of the flying head and near field light is generated so as to perform optical recording and reproduction
A schematic view of a near field optical information recording/reproduction device employing this kind of flying head is shown in FIG. 1. Here, a near field optical head 5 is fitted to the end of a suspension arm 10. The near field optical head 5 scans the surface of the recording medium 1 while floating a few tens of nanometers from the surface of the recording medium 1 due to air pressure received from a disc recording medium 1 rotating at high-speed. At the near field optical head 5, light from the laser light source (omitted from the drawings) is focussed at the lens so as to be made incident. The surface of the recording medium 1 and the near field optical head 5 mutually interact via the near field light so that scattered light generated as a result is taken as an output signal detected by an optical sensing element (not shown in the drawings).
However, because this kind of optical memory utilizes near field light, ultra-high density optical memory below the optical diffraction limit can be realized but unfortunately, on the other hand, the efficiency with which light can be utilized is lowered, and very little light is received by the light-receiving element.
In order to resolve this problem, in the related art, the intensity of the laser light employed is made strong or the conical structure of the plane probe constituting the near field light head is filled with a ball lens etc.
However, when the intensity of the laser light is increased, new problems with regards to heat generated and power consumed occur. Further, when a ball lens is employed, it is necessary to align the position of the ball lens which causes costs to increase. This has the result that it is difficult to adjust the focal point of light at an opening for all the near field optical heads during large-scale production due to variations in the individual ball lenses.
It is therefore also difficult to bring about ultra-high density memory utilizing near field light while maintaining low power consumption and mass production at a low price.
In order to resolve the problems of the method of the related art while increasing the efficiency with which light is utilized, it is the object of the present invention to implement a structure utilizing a plasma (hereinafter referred to as xe2x80x9cplasmonxe2x80x9d mechanism where optical energy is temporarily converted into plasmon energy of a metal particulate and is then converted back to being optical energy after passing through a microscopic region.
In order to achieve the aforementioned object, in the present invention, metal particulate is dispersed at at least part of a data mark of a recording medium for recording and reproducing information utilizing mutual interaction due to near field light generated by light incident to an optical head. Alternatively, metal particulate is dispersed at at least part of a data mark of a recording medium for recording and reproducing information utilizing mutual interaction due to near field light generated by light irradiating a recording medium. In other words, a layer dispersed with metal particulate taken as a date mark may be provided. Describing a specific structure in detail, a pattern of a light-blocking layer is formed on a transparent substrate, and a layer dispersed with metal particulate is formed on the transparent substrate at locations where the light-blocking layer is not provided.
According to this structure, the dispersed metal particulate receives energy during mutual interaction of incident light with the data mark of a size equal to or less than the wavelength of the incident light, and this energy is converted back to being light at a lower or upper part of the data mark, so that an output signal is amplified, an S/N ratio is improved and head scanning speed can be increased.
Alternatively, the dispersed metal particulate receives energy during mutual interaction of irradiating light passing through the data mark of a size equal to or less than the wavelength of the incident light, this energy is convened back to being light at a lower or upper part of the data mark, so that an output signal is amplified, an S/N ratio is improved and head scanning speed can be increased. The near field optical head therefore does not have to be irradiated with light of a substantial intensity and thermal damage to the head can be prevented.
Further, a material capable of generating a surface plasma as a result of light being incident to (or light irradiating) the metal particulate is employed.
According to this structure, energy due to incident light (or irradiating light) is received by a plasmon as a result of excitation of a plasmon at the surface of the metal particulate and this surface plasmon is then again converted into optical energy. As a result, the intensity of a signal generated by mutual interaction with a microscopic data mark smaller than the wavelength of incident light (or the wavelength of irradiating light) can be amplified, the S/N ratio can be improved, and the data transmission speed can be increased.
Further, the metal particulate can include at least one metal of Ag, Au, Cr, Al or Cu. A particle diameter of the metal particulate is from 1 nanometer to 50 nanometers, and a wavelength of the incident light or irradiating light is between 300 nanometers and 1 xcexcm.
Accordingly, a standard laser light source can be utilized for the incident light or irradiating light, and the metal particulate material can also be cheap. This means that mass production is possible at lower manufacturing costs.
The method for manufacturing a recording medium of the above structure comprises the steps of patterning a light-blocking layer on a transparent substrate, and forming a layer dispersed with metal particulate at locations where the light-blocking layer of the transparent substrate is not provided.
According to this invention, a highly efficient near field optical head can be manufactured with just a slight change in the manufacturing steps so that manufacture of a low-cost near field optical head is possible.
Further, there is provided a near field optical head for recording and reproducing information utilizing mutual interaction due to near field light generated by light incident to the near field optical head comprising a conical light-passing section formed at the substrate; an optical opening smaller than the wavelength of incident light formed at an end of the light-passing section; and a layer dispersed with metal particulate provided at at least part of the optical opening.
According to this structure, a near field optical head for recording and reproducing high-density information utilizing a related magnetic disc device configuration can be implemented. Further, because the optical efficiency of the near field optical head is high, an output signal of a sufficient intensity can be obtained without increasing the intensity of the incident light and a head where damage due to heating by the incident light can be avoided is realized. Further, the high optical efficiency brings about a high S/N ratio, and the data transmission speed can also be increased.
Further, there is provided a near field optical head for recording and reproducing information utilizing mutual interaction due to near field light generated by light incident to the near field optical head comprising a conical light-passing section formed at the substrate; an optical opening smaller than the wavelength of incident light formed at an end of the light-passing section; and a layer dispersed with metal particulate provided at least part of the optical opening.
According to this structure, a near field optical head for recording and reproducing high-density information utilizing a related magnetic disc device configuration can be implemented. Further, because the optical efficiency of the near field optical head is high, an output signal of a sufficient intensity can be obtained without increasing the intensity of the irradiating light and a head where damage due to heating by the irradiating light is avoided can be realized. Moreover, the high optical efficiency brings about a high S/N ratio, and the data transmission speed can also be increased.
Still further, a near field optical head for recording and reproducing information utilizing mutual interaction due to near field light generated by light incident to the near field optical head is formed with an optical opening smaller than or equal to the wavelength of light incident to the tip of a pointed light propagating body, with metal particulate being dispersed at part of the optical opening.
According to this structure, a near field head of a high optical efficiency can be made using a simple method, and a high data transmission speed can be implemented as a result of the high optical efficiency.
Further, in the present invention, there is provided an optical recording device for recording and reproducing information utilizing mutual interaction of near field light generated by light irradiating a recording medium and a near field optical head, wherein the near field optical head is equipped with a light-propagating body formed at an optical opening smaller than a wavelength of the irradiating light at a tip thereof, and a metal particulate is dispersed at the optical opening.
According to this structure, a near field head of a high optical efficiency can be made using a simple method, and a high data transmission speed can be implemented as a result of the high optical efficiency.
Further, the metal particulate is made of a material capable of generating a surface plasma as a result of the incidence or the irradiation of light.
Accordingly, energy of incident light or irradiating light is converted to energy of a surface plasmon of the metal particulate and propagated to a microscopic space in the shape of the plasmon so that energy can be propagated to the head in a highly efficient manner. As a result, a near field optical head of a high optical efficiency can be made and a high data transmission speed can be achieved.
Further, a method for manufacturing a near field optical head of the present invention comprises the steps of forming a conical hole in a substrate; forming a light blocking film at a side surface of the hole; and forming a layer dispersed with metal particulate in the vicinity of the opening.
According to this invention, a highly efficient near field optical head can be manufactured with just a slight change in the manufacturing steps.
Further, a further method for manufacturing a near field optical head of the present invention comprises the steps of: forming a tip part at a light propagating body; forming a light blocking film at the light propagating body with the exception of the tip part; and dispersing metal particulate at the tip part.
According to this invention, a highly efficient near field optical head can be manufactured with just a slight change in the manufacturing steps.